The level of leukotrienes B4 and C4 in the blood serum of rats subjected to thermal burns, x-irradiation and combined radiation-thermal injuries

In the present study the content of leukotrienes B4 and C4 (LTB and LTC) in rat serum was investigated. The changes in the leukotriene content after thermal burn was different from that after X-irradiation and combined effect of radiation and heat.     

The singling out of the dominant in white rats during the acquisition of a win-stay strategy in a 3-arm maze]

Correlation of shift and stay reactions was studied in rats in the process of singling out of the win-stay dominant. It was found that in rat which had no previous experience in receiving reinforcement in multi-arm maze, both the shifts and stay reactions were observed with the dominance of the shifts. In experienced rats formation of the win-stay strategy using a new direction required learning and had three stages: the stage of initial dominant, of displacements and of singling out a new dominant. Formation of a new protracted dominant of win-stay could be gradual (through formation of short-term dominants) or uneven. At repeated changes of the reinforcement place both the tendency to uneven transfer and delayed periods in formation of the protracted dominant were observed.     

X-ray structure and mechanism of ZgHAD,a l-2-haloacid dehalogenase from the marine Flavobacterium Zobellia galactanivorans

Haloacid dehalogenases are potentially involved in bioremediation of contaminated environments and few have been biochemically characterized from marine organisms. The l -2-haloacid dehalogenase (l -2-HAD) from the marine Bacteroidetes Zobellia galactanivorans Dsij^T (ZgHAD) has been shown to catalyze the dehalogenation of C2 and C3 short-chain l -2-haloalkanoic acids. To better understand its catalytic properties, its enzymatic stability, active site, and 3D structure were analyzed. ZgHAD demonstrates high stability to solvents and a conserved catalytic activity when heated up to 60°C, its melting temperature being at 65°C. The X-ray structure of the recombinant enzyme was solved by molecular replacement. The enzyme folds as a homodimer and its active site is very similar to DehRhb, the other known l -2-HAD from a marine Rhodobacteraceae. Marked differences are present in the putative substrate entrance sites of the two enzymes. The H179 amino acid potentially involved in the activation of a catalytic water molecule was confirmed as catalytic amino acid through the production of two inactive site-directed mutants. The crystal packing of 13 dimers in the asymmetric unit of an active-site mutant, ZgHAD-H179N, reveals domain movements of the monomeric subunits relative to each other. The involvement of a catalytic His/Glu dyad and substrate binding amino acids was further confirmed by computational docking. All together our results give new insights into the catalytic mechanism of the group of marine l -2-HAD.     

Peculiarities of summation processes in visual-sensitive neurons in the pretectal area of cat

Summation processes occurring in single neurons of the pretectal area in response to either moving or stationary light stimuli were studied in acute experiments on cats. In most neurons studied (85%), gradual increase of the angular size of stimulus resulted in clearly defined summation. In neurons lacking directional sensitivity (nondirectional neurons) the stimulus movement in two opposite directions caused, as a rule, similar and symmetrical changes in the number of spikes, whereas under the same conditions direction-sensitive neurons, in addition to symmetrical development of summation processes, could exhibit substantial differences in the summation curves. The responses to a preferred movement direction could be significantly inhibited or facilitated, while the responses to a non-preferred direction remained stable or changed reciprocally. Neuronal responses to different directions of the movement of stimulus might change independently of each other. This was also the case whenon andoff responses of theon—off neurons to stationary stimuli were compared. It is concluded that neurons of the pretectal area have a complex infrastructure of receptive fields that significantly influences the integration of incoming information.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 376–382, September–October, 1993.     

Proliferation of the cells of iris and pigment epithelium of the retina in the early periods after removal of the lens and iris in Spanish newts]

It has been shown by means of autoradiography that following the simultaneous removal of lens and retina in the eyes of adult ribbed newts (Pleurodeles waltlii) the proliferative processes related to the regeneration of retina, rather than lens, are most active at the early stages of eye restoration. During the lens regeneration in the absence of retina, the proliferation of the cells of pars iridica of the dorsal iris zone, a source of lens regeneration, is delayed, possibly due to the increase of the duration of mitotic cycle of these cells.     

The effects of influence of electromagnetic irradiation of millimeter wavelength on background impulse activity of supraoptic nucleus' neurons of rats' hypothalamus

In conditions of acute experiment on white rats anaesthetized by Nembutal (40 mg/kg, intraperitoneally), the registration and analysis of background impulse activity of the supraoptic nucleus neurons of rats' hypothalamus in norm and after electromagnetic irradiation of millimeter wavelength on organism, were carried out. Distributions of neurons by the degree of rhythm regularity, the character of types of dynamics of the following impulse flows, the modality of histograms of interspike intervals, the average discharge frequency, the coefficient of interspike intervals variation, were found out. Changes of the background impulse activity which were related mainly to the changes of the inner structure of registered impulse flows, were revealed. Significant shifts were generally observed in the character of dynamics of neuronal current flows and degree of regularity of the impulse activity. Statistically significant changes of the average frequency of discharges of different frequency range neurons' populations were revealed.     

Crystallization of three key glycolytic enzymes of the opportunistic pathogen Cryptosporidium parvum

Cryptosporidium parvum is one of the major causes of waterborne diseases worldwide. This protozoan parasite depends mainly on the anaerobic oxidation of glucose for energy production. In order to identify the differences in the three-dimensional structure of key glycolytic enzymes of C. parvum and its human host, we have expressed, purified and crystallized recombinant versions of three important glycolytic enzymes of the parasite, namely, glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase and lactate dehydrogenase. Lactate dehydrogenase has been crystallized in the absence and in the presence of its substrates and cofactors, while pyruvate kinase and glyceraldehyde 3-phosphate dehydrogenase were crystallized only in the apo-form. X-ray diffraction data have been collected for all crystals.     

Extraordinarily stable disulfide-linked homodimer of human growth hormone

Although a 22-kDa human growth hormone (hGH) is the predicted protein product of the hGH-N gene, a pleiotropic collection of uncharacterized molecular weight and charge isoforms is also produced. Using chromatography and preparative SDS-PAGE under reducing conditions we isolated an unusually stable mercaptoethanol-resistant (MER) 45-kDa hGH. A 5-h incubation at 100 degrees C in the presence of 2-mercaptoethanol was required to convert approximately 90% of MER-45-kDa hGH into a 22-kDa hGH. Other reductants were not as effective in splitting MER-45-kDa hGH. After fracturing MER-45-kDa hGH, the 22-kDa hGH fragments would spontaneously reassociate if the reductant was removed; however, alkylation of cysteine residues prevented their reassociation. Identical amino acid sequences for the first six N-terminal residues were obtained for MER-45-kDa hGH and its 22-kDa hGH cleavage product. Structural identity of MER-45-kDa hGH and 22-kDa hGH was demonstrated by MALDI-TOF mass spectrometry of tryptic digests. MER-45-kDa hGH did not break up upon incubation with EDTA and EGTA. The significance of this work to our understanding of the structure of hGH isoforms is that it demonstrates that MER-45-kDa hGH is not a single chain polypeptide but is instead a homodimer of 22-kDa hGH monomers. The MER-45-kDa hGH dimer is held together by interchain disulfide bonds and not by divalent metal cation bridges. Additionally, MER-45-kDa hGH's interchain disulfide links are exceptionally resistant to reducing agents and thus confer extreme stability to the homodimer.